Communication devices such as wireless devices and terminals are also known as e.g. User Equipments (UE), mobile terminals, stations (STAs), wireless terminals and/or mobile stations. Terminals are enabled to communicate wirelessly in a wireless communications network or a cellular communication system, sometimes also referred to as a cellular radio system or cellular networks. The communication may be performed e.g. between two terminals, between a terminal and a regular telephone and/or between a terminal and a server via a Radio Access Network (RAN) and possibly one or more core networks, comprised within the cellular communications network.
Terminals may further be referred to as mobile telephones, cellular telephones, laptops, or surf plates with wireless capability, just to mention some further examples. The terminals in the present context may be, for example, portable, pocket-storable, hand-held, computer-comprised, or vehicle-mounted mobile devices, enabled to communicate voice and/or data, via the RAN, with another entity, such as another terminal or a server.
The cellular communications network covers a geographical area which is divided into cell areas, wherein each cell area being served by an access node such as a base station, e.g. a Radio Base Station (RBS), which sometimes may be referred to as e.g. “eNB”, “eNodeB”, “NodeB”, “B node”, or Base Transceiver Station (BTS), depending on the technology and terminology used. The base stations may be of different classes such as e.g. macro eNodeB, home eNodeB, micro eNodeB or pico base station, based on transmission power, functional capabilities and thereby also cell size. A cell is the geographical area where radio coverage is provided by the base station at a base station site. One base station, situated on the base station site, may serve one or several cells. Further, each base station may support one or several communication technologies. The base stations communicate over the air interface operating on radio frequencies with the terminals within range of the base stations. In the context of this disclosure, the expression Downlink (DL) is used for the transmission path from the base station to the mobile station. The expression Uplink (UL) is used for the transmission path in the opposite direction i.e. from the mobile station to the base station.
In 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE), base stations, which may be referred to as eNodeBs or even eNBs, may be directly connected to one or more core networks.
3GPP LTE radio access standard has been written in order to support high bitrates and low latency both for uplink and downlink traffic. All data transmission is in LTE controlled by the radio base station.
The RRC protocol is responsible for the establishment, maintenance and release of the Radio resource Control (RRC) connection between the UE and a Universal Terrestrial Radio Access Network (UTRAN) as well as the establishment, reconfiguration and release of Radio Bearers (RBs) and Signaling Radio Bearers (SRBs).
UTRAN is a collective term for the base stations and Radio Network Controllers (RNCs) which make up an Universal Mobile Telecommunications System (UMTS) radio access network.
Different RRC procedures like for example RB Setup, RB Release and RB Reconfiguration may be used to reconfigure the Radio Access Bearer (RAB-), RB/SRB-, transport channel- and physical channel parameters in the UE from a “source configuration” to a “target configuration”. The reconfiguration is typically triggered by data activity, e.g. transmission of data, and/or inactivity of existing radio bearers or by setup and/or release of new radio bearers.
When the same action is repeated multiple times, e.g. at transmission of small amount of data, the UE will typically toggle, e.g. switch, between a limited set of configurations. Typically, the UTRAN needs to signal the new target configuration for each transition.
The following methods to signal a new target configuration to the UE are currently known according to the prior art:
Complete Configuration:
a full set of the above parameters specifying the target configuration, or a subset of the parameters representing a delta, e.g. a difference, between the source configuration and the target configuration, is included in the RRC message. This option may be used for most of the RRC procedures and is the commonly used method today.
Predefined Configurations:
Instead of signaling the complete configuration, the RRC message contains an identifier of one predefined configuration that the UE has already acquired via a System Information block (SIB), e.g. SIB16.
Default configuration: Instead of signaling the complete configuration, the RRC message contains an identifier to one of the default configurations specified by 3GPP in 25.331. Default configurations are only available for Circuit Switched (CS) radio bearers and stand-alone signaling radio bearers. There are no default configurations for Packet Switched (PS) bearers.
The methods relating to predefined and default configurations mentioned above may only be applied for the following RRC messages:                RRC Connection Setup message        Handover to UTRAN Command message        RB Reconfiguration message (only in case the message is sent through GSM EDGE Radio Access Network (GERAN) Iu mode)        
A drawback with the above-described first method of signaling the complete target configuration, is that it will generate large RRC messages which may impact both latency and retainability, e.g. by increasing the latency and reducing the retainability, especially in bad radio condition or at the cell border. Signaling of delta configurations will reduce the message size to some extent but may on the other hand lead to a dropped call as a result of inconsistent configuration in the UE. A drawback with the above-described second and third methods, of using predefined configurations and default configurations, respectively, is that the number of use-cases where these configurations can be applied is very limited, e.g. only at RRC Connection Setup and Incoming Inter-Radio Access Technology (IRAT) Handover. The number of available configurations is also limited. Default configurations are only specified for CS bearers and stand-alone SRBs, and cannot be used for PS bearers. Even if UTRAN can specify its own predefined configurations in SIB16 the number of configurations must be limited in order to reduce the size of information sent on the broadcast channel. A large SIB16 may impact the overall SIB acquisition time and increase latency for other use-cases like for example call setup and cell reselection. Overall the predefined and default configurations have shown to be too inflexible and have not been used much. There is also limited support for these methods in the UEs.
In 3GPP release 13 a method for storing and re-using parameters in RRC signaling is introduced With this method, the first time a specific configuration is to be applied, the UTRAN sends an RRC message to the UE, e.g. the UTRAN sends a Radio Bearer Reconfiguration message with a set of parameters specifying the new target configuration. In addition to the configuration parameters an identity, e.g. a number, is included in the message. At reception of the message, the UE shall store the values of the defined set of parameters and associate the configuration with the identity included in the message. FIG. 1 illustrates the concept of stored configurations, which configurations sometimes are referred to as retrievable configurations. The figure shows how a wireless device, e.g. the above-mentioned UE, may store a number of configurations. When the UE is reconfigured from one configuration to another, only the target identity needs to be signaled, as the UE has all parameters stored for that configuration.
Next time the UTRAN wants to use the same configuration, only the identity needs to be included in the message. Both the UTRAN and the UE have stored the parameter values specifying the target configuration so this information does not have to be sent again. This method reduces the amount of signaling needed to the UE. However, a drawback with the method is that by using the concept for retrievable configurations, there is a risk that the number of configurations that the wireless device, e.g. the UE, would have to store is larger than what is practically possible. Defining new configurations may also add unnecessary overhead as the delta configuration compared to the currently used source configuration must be provided in the RRC message.